Signs of 'Reverse Spin Bias' Found in Medical Cannabis Studies

What is Reverse Spin Bias?

This bias is called "reverse spin bias." It occurs when authors of systematic reviews downplay or overlook the positive outcomes of a treatment, even when their findings suggest significant benefits.

The research, published in the journal *Research Integrity and Peer Review*, looked into 29 systematic reviews on medical cannabis used for pain management. The researchers found that 10 of these reviews showed reverse spin bias. In these cases, despite the evidence hinting at potential benefits of cannabis, the authors either didn't support its use or raised doubts about its effectiveness. Instead of highlighting the positive results, they framed the information in a way that downplayed these findings.

For example, they often described the evidence as "inconsistent," claimed it was based solely on low-quality studies, or even stated that there weren’t enough studies to conclude, regardless of the actual number of studies available. Some authors also employed alarming language about "unknown future harms" to downplay the benefits, even when no data indicated negative effects.

The study points out that reverse spin bias is similar to what we traditionally know as spin bias, where findings are exaggerated. This new bias seems to be driven by the perception that journals prefer to publish studies that only show negative outcomes related to cannabis, which limits the visibility of evidence presenting a different perspective.

The implications of reverse spin bias are widespread. For instance, a charity called Drug Science noted that this type of bias could significantly influence drug policy and harm reduction discussions. When studies understate the benefits of controversial treatments like medical cannabis, the resulting policies might seem to be based on sound evidence. Still, they can actually be swayed by public opinion and stigma.

The study also raises concerns that reverse spin bias might appear in other controversial therapies, such as safe opioid consumption sites. The researchers stress that recognising this bias is crucial for ensuring drug policies are based on genuine evidence rather than societal biases.

What Needs to be Done to Avoid Reverse Spin Bias?

To address this issue, the researchers urge for more investigations into reverse spin bias and recommend that editors and peer reviewers of medical journals remain watchful for inconsistencies between the outcomes of systematic reviews and the recommendations made by the authors. This vigilance could help ensure that medical evidence is reported accurately and fairly.

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